The goal of the research program is to understand the mechanisms involved in the coordination and control of DNA replication, chromosome segregation and cell division. Our approach has been to isolate, purify and characterize the DNA polymerase activities from human tissues, and to this end we have employed the continuous cell line KB and, more recently, fresh human liver obtained from cardiac transplant donors at the time of surgery. In our studies of KB cells, we have described the properties of DNA polymerase Beta, which we have purified to homogeneity, and the properties of a very highly purified form of DNA Polymerase alpha. We have continued our efforts to obtain a pure preparation of polymerase alpha, and recently developed steps suggest that this objective will soon be accomplished. More recently, we described an apparently unique species of DNA polymerase from the purified nuclear fraction of KB cells. Our recent studies of human liver suggest that the purified nuclear fraction contains a predominant polymerase activity that appears at this still preliminary stage of the project to be very similar to the new species observed in KB cells. This study has also indicated that the nuclear DNA polymerase activity that has recently been assumed to be predominantly polymerase alpha may in fact be a mixture of alpha with the new activity, and possibly polymerase gamma as well, and at least in the normal adult (non-proliferating) organ, the new polymerase may in fact be the predominant nuclear species. Finally, we have initiated a study of the DNA polymerase activities in several varieties of mycoplasma, and initial results suggest that these peculiar organisms contain two activities, neither of which closely resembles the polymerases that have been described to date from mammalian and human cells. The mycoplasma enzymes are themselves of interest, particularly since they appear to contain no associated nuclease activities, thus differing in a fundamental manner from the DNA polymerases that have thus far been recognized from prokaryotes. BIBIBLIOGRAPHIC REFERENCES: Sedwick, W.D., Wang, T.S-F., and Korn, D.: Cytoplasmic DNA Polymerase: Structure and Properties of the Highly Purified Enzyme from Human KB Cells. J. Biol. Chem., 250, 7045-7056 (1975).